1. Field of the Invention:
This invention relates generally to vacuum circuit interrupters and more particular to vacuum circuit interrupters having high voltage vacuum monitoring devices which utilize leakage currents between metallic parts to indicate abnormal pressure conditions within the vacuum circuit interrupter.
2. Description of the Prior Art:
Vacuum circuit interrupters are generally comprised of a pair of separable contacts operated within an evacuated enclosure. Typically, the internal portion of the enclosure is evacuated to a pressure of 10.sup.-4 torr or less. The vacuum has a high dielectric strength per unit distance of separation between the separable contacts to efficiently extinguish arcs generated upon opening the contacts. The high dielectric strength maintained by the vacuum sufficiently prevents restriking of the arc once separation has been made. To ensure sufficient and safe operation of vacuum circuit interrupters, it is required that the pressure within the enclosure be kept below a predetermined value to maintain the dielectric strength required.
It is known in the prior art to use vapor deposition shields within the evacuated enclosure as a means of detecting leakage currents within the circuit interrupter under abnormal pressure conditions. For example, U.S. Pat. No. 3,263,162 entitled "Apparatus and Method for Measuring the Pressure Inside a Vaccum Interrupter" by J. R. Lucek et al. and U.S. Pat. No. 3,403,297 entitled "Vaccum-Type Circuit Interrupters with Pressure Monitoring Means" by D.W. Crouch teach such methods. Additionally, U.S. Pat. No. 4,351,992 entitled "High Potential Testing of Vacuum-type Circuit Interrupters" issured to D. W. Crouch teaches monitoring means for vacuum circuit interrupters having a metallic housing. However, power engineers continue to seek more effective and efficient ways to monitor the vacuum in vacuum circuit interrupters.